Ink for printing, printed matter, printing method and printer

ABSTRACT

The printing ink of the present invention is characterized by containing a photo-curable high polymer precursor, and a photopolymerization initiator, and containing 3 to 8 parts by weight of inorganic fine particles having a mean particle size of 0.1 μm or less to 100 parts by weight of the high polymer precursor. Moreover, the printing ink of the present invention is characterized by having a viscosity at a shear rate of 5 (l/s) of 8 to 75 (Pa·s), a viscosity at a shear rate of 20 (l/s) of 3 to 25 (Pa·s), and a thixotropic index value of 1.5 to 3.5. As a result of using this printing ink, letters, figures, symbols, graphics, etc., having a thickness of 0.2 mm or more can be printed rapidly without affecting the printed base material. In addition, as a result of using the printing ink of the present invention, a printed matter of the present invention can be provided that is characterized by the printing ink of the present invention being printed onto the surface of the printed base material followed by curing. In particular, the present invention is preferable for obtaining a Braille printed matter, and the Braille printed matter in which Braille characters are printed on the surface can be provided by printing the printing ink of the present invention onto the surface of the printed base material in the form of dots followed by curing.

TECHNICAL FIELD

[0001] The present invention relates to a printing ink enablinghigh-speed printing of letters, figures, symbols, graphics, etc., havinga thickness of 0.2 mm or more without having an effect on the printedbase material. In addition, the present invention relates to a printedmatter obtained using this printing ink, a printing method for printingusing this printing ink, and a printer suitable for use when printingusing this printing ink.

BACKGROUND ART

[0002] Embossing, in which a specific location of a base material ismechanically deformed by pressing from the back to the front, is knownas one technology used to form letters, figures, symbols, graphics,etc., having a thickness of 0.2 mm or more, such as Braille charactersfor persons with vision or hearing disabilities, card numbers and names,on the surface of cards and other base materials.

[0003] However, in the case of technology in which letters and so forthhaving a thickness of 0.2 mm or more are formed by embossing, since itis necessary to mechanically deform the base material, together withthere being restrictions on the material of the base material used,there is the risk of damaging the base material when performingembossing. In addition, although so-called IC cards containing internalIC, wiring patterns and so forth have been developed in recent years, inthe case of performing embossing on base materials like these, there isthe risk of causing disconnection of the IC, wiring patterns and soforth contained within.

[0004] Therefore, thick film printing by screen printing has beenemployed in the past as a method for obtaining letters and so forthhaving a thickness of 0.2 mm or more without placing restrictions on thebase materials used and without having an effect on the base material.In addition, thick film printing using an ink jet system has also beenproposed in recent years.

[0005] In the case of screen printing, however, the upper limit on thefilm thickness that can be printed in a single printing is severalmicrometers to several tens of micrometers, thereby resulting in theproblem of being unable to obtain a thick film of 0.2 mm or more unlessprinting is repeated several times.

[0006] In addition, as an example of thick film printing using an inkjet system, Japanese Unexamined Patent Application, First PublicationNo. 2000-37943 discloses a method for performing thick film printing byan ink jet system using an ultraviolet curable ink having a surfacetension greater than or equal to the wetting index of the printed basematerial. However, in the case of the method disclosed in JapaneseUnexamined Patent Application, First Publication No. 2000-37943, it isdifficult to obtain a stable thick film of the desired shape as a resultof the shape of the coated ink being affected depending on the wettingindex of the surface of the printed base material. In addition, in thecase of thick film printing using an ink jet system, since it isdifficult to discharge the ink unless the ink has a low viscosity ascompared with screen printing, it is even more difficult to obtain athick film.

[0007] In addition, since the photo-curable ink for thick film printingused in conventional thick film printing is required to be cured usingan intense ultraviolet light source such as a mercury lamp, there is therisk of the base material being damaged by the ultraviolet light andheat. In addition, since ultraviolet radiation units using an intenseultraviolet light source such as a mercury lamp are large, a portable,compact printer for thick film printing has not been developed.

DISCLOSURE OF THE INVENTION

[0008] Therefore, in consideration of the above circumstances, an objectof the present invention is to provide a printing ink that enableshigh-speed thick film printing without having an effect on a printedbase material. In addition, an object of the present invention is toprovide a printed matter obtained using this printing ink, a printingmethod for printing using this printing ink, and a compact printersuitable for use when printing using this printing ink.

[0009] The inventors of the present invention conducted studies byfocusing on the points described below in order to solve these problems.

[0010] Although it is possible to print inks having a wide range ofviscosity by using a dispenser, the speed of thick film printing cannotbe increased simply by focusing on ink viscosity alone. That is,although the film thickness that can be formed in a single printing canbe increased the higher the viscosity of the ink, the increases in theviscosity of the ink causes a decrease in the ink discharge rate, as aresult of which the problem of slower printing speed occurs.

[0011] Therefore, in order to obtain a thick film in a single printingwithout causing the decrease in the ink discharge rate, the inventors ofthe present invention found that an ink is suitable in which, togetherwith the viscosity decreasing during ink discharge, the viscosityincreases after printing onto the surface of a print ed base material,namely, a thixotropic ink in which the viscosity decreases by applyingshear stress (shearing stress) and increases by allowing to standundisturbed following the application of the shear stress.

[0012] Moreover, the inventors of the present invention also found that,even in the case of the thixotropic ink, depending on the viscosityimmediately after discharge and the degree of the thixotropy, it isdifficult to obtain a thick film having a satisfactory shape in a singleprinting without lowering the ink discharge rate.

[0013] That is, it was found that, even in the case of the thixotropicink, the increase in the viscosity after being discharged onto theprinted base material is small in the case of the ink in which theviscosity immediately after discharge and the thixotropy are somewhatlow, and as a result, the ink spreads excessively to the surroundingarea after being discharged onto the printed base material, therebymaking it difficult to obtain a thickness of 0.2 mm or more.

[0014] Conversely, it was also found that, since the increase in theviscosity immediately after discharge is remarkably high in the case ofthe ink having somewhat high thixotropy, together with the ink dischargerate decreasing to an extent to which it is no longer practical, the inkdoes not spread after being discharged onto the printed base materialand the ends become pointed, thereby making it difficult to obtain athick film of a desired shape.

[0015] Therefore, as a result of specifying viscoelasticcharacteristics, the inventors of the present invention discovered aprinting ink as described below that enables the obtaining of a thickfilm of satisfactory shape having a thickness of 0.2 mm or more in asingle printing without causing a decrease in the ink discharge rate,thereby leading to completion of the present invention.

[0016] The printing ink of the present invention is characterized bycontaining a photo-curable high polymer precursor and aphotopolymerization initiator, and together with, at 25° C., theviscosity at a shear rate of 5 (l/s) being 8 to 75 (Pa·s), the viscosityat a shear rate of 20 (l/s) is 3 to 25 (Pa·s), and the thixotropic indexvalue is 1.5 to 3.5.

[0017] In the present description, “thixotropic index value” is definedas the “ratio of viscosity at a shear rate of 5 (l/s) to viscosity at ashear rate of 20 (l/s)”. Furthermore, the thixotropic index value is anindicator of thixotropy, and the larger this value, the greater thethixotropy.

[0018] The printing ink of the present invention has thixotropy suchthat the viscosity decreases the greater the shear stress that isapplied (the larger the shear rate), and that the viscosity increases byallowing it to stand undisturbed following the application of the shearstress.

[0019] Moreover, the printing ink of the present invention ischaracterized by, at 25° C., having a viscosity of 8 to 75 (Pa·s) at ashear rate of 5 (l/s), a viscosity of 3 to 25 (Pa·s) at a shear rate of20 (l/s), and a thixotropic index value of 1.5 to 3.5. By defining theviscosity relative to the shear rate and the thixotropic index value inthis manner, the inventors of the present invention found that a thickfilm having a favorable shape and a thickness of 0.2 mm or more can beobtained in a single printing without causing a decrease in the inkdischarge rate.

[0020] Furthermore, the inventors of the present invention also foundthat, in which, at 25° C., the viscosity at a shear rate of 5 (l/s), theviscosity at a shear rate of 20 (l/s), and the thixotropic index valueare less than the lower limits defined above, there is a risk of beingunable to obtain the desired thick film due to excessive spreading ofthe ink after being coated onto the surface of the printed basematerial.

[0021] On the other hand, in a case in which, at 25° C., the viscosityat a shear rate of 5 (l/s), the viscosity at a shear rate of 20 (l/s),and the thixotropic index value exceed the upper limits defined above,it was found that the ink discharge rate decreases to an extent to whichit is no longer practical. In addition, in the case, at 25° C., theviscosity at a shear rate of 5 (l/s), the viscosity at a shear rate of20 (l/s), and the thixotropic index value exceed the upper limitsdefined above, it was found that there is a risk of it becomingdifficult to obtain a thick film of the desired shape due to the inkfailing to spread after being discharged onto the surface of the printedbase material resulting in the formation of sharp ends.

[0022] In addition, the inventors of the present invention also foundthat the thixotropic printing ink can be obtained by containinginorganic fine particles in a printing ink and then dispersing in theform of a colloid.

[0023] In the printing ink of the present invention, inorganic fineparticles are thought to be uniformly dispersed in the state in which aplurality of fine particles are aggregated within a range over whichthey do not precipitate, and the thixotropy is thought to be expressedin which the viscosity of the ink decreases as a result of theaggregated inorganic fine particles mutually separating due to theapplication of the shear stress, while the viscosity increases as aresult of a plurality of inorganic fine particles again aggregating dueto the reduction or elimination of the shear stress after the shearstress has been applied.

[0024] In addition, it is preferable to use inorganic fine particleshaving a mean particle size of 0.1 μm or less. By using the microscopicinorganic fine particles having a mean particle size of 0.1 μm or less,even if a plurality of the inorganic fine particles aggregate, theentire aggregated inorganic fine particles do not become excessivelylarge, thereby making it possible to prevent the inorganic fineparticles from being non-uniformly dispersed or precipitating in theprinting ink. In addition, the inorganic fine particles are preferablycontained at 3 to 8 parts by weight relative to 100 parts by weight ofthe high polymer precursor. It was found that, by setting theconcentration of the inorganic fine particles in this manner, theprinting ink of the present invention can be obtained having theviscoelastic characteristics described above.

[0025] Furthermore, the inventors of the present invention found that,if the concentration of the inorganic fine particles is less than 3parts by weight, at 25° C., the viscosity at a shear rate of 5 (l/s),the viscosity at a shear rate of 20 (l/s), and the thixotropic indexvalue become smaller than the previously defined lower limits. Inaddition, in the case in which the concentration of the inorganic fineparticles exceeds 8 parts by weight, it was found that, at 25° C., theviscosity at a shear rate of 5 (l/s), the viscosity at a shear rate of20 (l/s) and the thixotropic index value exceed the previously definedupper limits.

[0026] Furthermore, in the case of using a plurality of types of thehigh polymer precursors, the statement “inorganic fine particles arecontained at 3 to 8 parts by weight in 100 parts by weight of the highpolymer precursor” means that “inorganic fine particles are contained at3 to 8 parts by weight relative to 100 parts by weight defined as thetotal blended amount of all high polymer precursors.”

[0027] In addition, it is preferable that the printing ink of thepresent invention transmits light after curing. The use of such aconstitution makes it possible to prevent letters, figures, symbols,etc., printed on the surface of the printed base material prior to thickfilm printing from being obscured due to thick film printing.

[0028] The following printed matter and printing method of the presentinvention can be provided by using the printing ink of the presentinvention as described above.

[0029] The printed matter of the present invention is characterized bythe printing ink containing a photo-curable high polymer precursor and aphotopolymerization initiator, and at 25° C., having a viscosity of 8 to75 (Pa·s) at a shear rate of 5 (l/s), a viscosity of 3 to 25 (Pa·s) at ashear rate of 20 (l/s), and a thixotropic index value of 1.5 to 3.5,being printed on the surface of a printed base material followed bycuring.

[0030] In addition, the printing ink preferably contains inorganic fineparticles. Here, the printing ink preferably further contains 3 to 8parts by weight of inorganic fine particles relative to 100 parts byweight of the high polymer precursor. In addition, the mean particlesize of the inorganic fine particles is preferably 0.1 μm or less. Inaddition, the inorganic fine particles are preferably dispersed in theprinting ink in the form of a colloid. In addition, the printing inkpreferably transmits light after curing.

[0031] The present invention is particularly preferable for obtainingBraille printed matter, and by printing the printing ink of the presentinvention on the surface of the printed base material in the form ofdots followed by curing, Braille printed matter can be provided in whichBraille characters are printed on the surface.

[0032] In addition, by printing the printing ink of the presentinvention on the surface of the printed base material in the form ofletters, figures or symbols followed by curing, a printed matter can beprovided in which names, figures and so forth having a thickness of 0.2mm or more are printed on the surface of a printed base material.

[0033] Although any material or shape may be used for the printed basematerial, cards imprinted with names, card numbers, etc., for example,a-re preferable. In addition, the present invention is also particularlypreferable in the case of using for the printed base material cards suchas IC cards for which there is the risk of disconnection of internal ICor wiring patterns when subjected to embossing.

[0034] In addition, the printing method of the present invention ischaracterized by having a step of printing the printing ink of thepresent invention onto the surface of the printed base material using adispenser and a step of curing the printing ink printed onto the surfaceof the printed base material by exposing to light.

[0035] Moreover, the inventors of the present invention invented aportable, compact printer suitably used when performing thick filmprinting using the printing ink of the present invention.

[0036] The printer of the present invention is characterized by beingprovided with an ink discharge unit having a discharge port thatdischarges a photo-curable printing ink, a base material holding unitthat holds a printed base material, a position control unit capable ofarranging in opposition at a prescribed interval the discharge port ofthe ink discharge unit and a prescribed position on the surface of theprinted base material held by the base material holding unit, and alight emitting unit that cures the printing ink by emitting light ontothe printing ink discharged from the ink discharge unit onto the surfaceof the printed base material, wherein the ink discharge unit, the basematerial holding unit, the position control unit and the light emittingunit are all contained in a single rack.

[0037] In addition, in the printer of the present invention, the inkdischarge unit is characterized by containing a dispenser having an inkcylinder filled with the printing ink inside.

[0038] In addition, the light emitting unit is characterized by beingable to radiate ultraviolet light of 1500 to 5000 μW/cm².

[0039] In the case of conventional thick film printing, since an intenseultraviolet light source such as a mercury lamp was used, a printercontaining a built-in light emitting unit has yet to be developed. Incontrast, in the case of the present invention, since the ink that isused can be cured with ultraviolet light of low intensity, by composingthe light emitting unit using a compact ultraviolet light source capableof emitting ultraviolet light of low intensity of 1500 to 5000 μW/cm², aportable, compact printer is realized in which the ink discharge unit,the base material holding unit, the position control unit, and the lightemitting unit are all contained in a single rack.

[0040] In addition, by composing the light radiation unit using anultraviolet light source capable of emitting ultraviolet light of lowintensity of 1500 to 5000 μW/cm², damage to the printed base materialcaused by ultraviolet light and heat can be reduced.

[0041] The printer of the present invention is preferably used whenperforming thick film printing using the printing ink of the presentinvention. However, since the dispenser is capable of discharging inkshaving a wide range of the viscosity, and various other means (such asan ink jet system) other than a dispenser can be employed for the inkdischarge unit, the printer of the present invention can be applied evenin the case of performing printing using various inks other than theprinting ink of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042]FIG. 1 is a schematic cross-sectional view showing the structureof a printer of one embodiment according to the present invention.

[0043]FIG. 2 is a graph showing the relationship between the shear rateand the viscosity for a printing ink obtain in Embodiment 1 according tothe present invention.

[0044]FIG. 3 is a graph showing the relationship between the shear rateand the viscosity for various printing inks obtained in Examples 1through 6 according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0045] The following provides a detailed explanation of the presentinvention.

[0046] Printing Ink

[0047] First, an explanation is provided of a printing ink of thepresent invention.

[0048] The printing ink of the present invention is characterized bycontaining a photo-curable high polymer precursor, a photopolymerizationinitiator and inorganic fine particles at a prescribed concentration,and at 25° C., the viscosity at a shear rate of 5 (l/s) being 8 to 75(Pa·s), the viscosity at a shear rate of 20 (l/s) being 3 to 25 (Pa·s),and the thixotropic index value being 1.5 to 3.5. In addition, theinorganic fine particles are dispersed in the printing ink of thepresent invention in the form of a colloid.

[0049] As a result of employing the above constitution, a thick film ofa satisfactory shape of 0.2 mm or more can be obtained in a singleprinting without decreasing the discharge rate of the ink.

[0050] Furthermore, in the case, at 25° C., the viscosity at a shearrate of 5 (l/s), the viscosity at a shear rate of 20 (l/s), and thethixotropic index value are smaller than the lower limits defined above,there is the risk of it becoming difficult to obtain the desired thickfilm due to the ink spreading excessively after being coated onto thesurface of a printed base material.

[0051] On the other hand, in the case in which, at 25° C., the viscosityat a shear rate of 5 (l/s), the viscosity at a shear rate of 20 (l/s),and the thixotropic index value exceed the upper limits defined above,the discharge rate of the ink decreases to an extent to which it is nolonger practical. In addition, in the case in which, at 25° C., theviscosity at a shear rate of 5 (l/s), the viscosity at a shear rate of20 (l/s), and the thixotropic index value exceed the upper limitsdefined above, the ink does not spread after being discharged onto theprinted base material and the ends become pointed, thereby resulting inthe risk of it becoming difficult to obtain a thick film of a desiredshape.

[0052] In the printing ink of the present invention described above, aphoto-curable high polymer precursor refers to a “photo-curable monomer”or a “photo-curable prepolymer for which the degree of polymerization ofa photo-curable oligomer and so forth is low and which is polymerizeddue to the progression of a curing reaction”, and one type or aplurality of types of known photo-curable monomers or prepolymers can beused.

[0053] Examples of the photo-curable monomers include urethane-basedacrylate monomers, ester-based acrylate monomers, and epoxy-basedacrylate monomers. Examples of photo-curable prepolymers includeurethane-based acrylate prepolymers, ester-based acrylate prepolymers,and epoxy-based acrylate prepolymers.

[0054] Examples of photopolymerization initiators include acetophenone,2,2-diethoxyacetophenone, p-dimethylaminoacetophenone,p-dimethylaminopropiophenone, benzophenone, 2-chlorobenzophenone,pp′-dichlorobenzophenone, pp′-bisdiethylaminobenzophenone, Michler'sketone, benzyl, benzoin, benzoinmethylether, benzoinethylether,benzoinisopropylether, benzoin-n-propylether, benzoinisobutylether,benzoin-n-butylether, benzyldimethylketal,tetramethylthiorammonosulfide, thioxansone, 2-chlorothioxanzone,2-methylthioxansone, azobisisobutyronitrile, benzoinperoxide,di-t-butylperoxide, 1-hydroxycyclohexylphenylketone,2-hydroxy-2-methyl-1-phenyl-1-one,1-(4-isopropylphenhyl)-2-hydroxy-2-methylpropane-1-one,methylbenzoylformate and2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropane-1-one.

[0055] In addition, inorganic fine particles of any materials may beused for the inorganic fine particles, examples of which include one ora plurality of types of inorganic fine particles containing carbonblack, aluminum oxide, iron oxide or silicon oxide.

[0056] The mean particle size of the inorganic fine particles ispreferably 0.1 μm or less. By using microscopic inorganic fine particleshaving a small mean particle size like this, even if a plurality ofinorganic fine particles aggregate, the entire aggregated inorganic fineparticles do not become excessively large, thereby making it possible toprevent the inorganic fine particles from being non-uniformly dispersedor precipitating in the printing ink.

[0057] In addition, inorganic fine particles are preferably contained at3 to 8 parts by weight relative to 100 parts by weight of the highpolymer precursor. By blending the inorganic fine particles in thismanner, the printing ink of the present invention can be provided thathas the viscoelastic characteristics described above.

[0058] In addition, it is preferable that the printing ink of thepresent invention transmits light after curing, and it is particularlypreferable that it be transparent after curing. As a result of composingin this manner, it is possible to prevent letters, figures, symbols,etc., printed on the surface of the printed base material prior to thickfilm printing from becoming illegible due to thick film printing.

[0059] In addition, the printing ink of the present invention may beblended with various additives such as curing accelerators, pigments,dyes, resins, salts or acids in addition to those previously described.In particular, it is desirable to blend a curing accelerator such as abenzyldimethylketal-based sensitizer to enable curing even with light oflow intensity.

[0060] Printed Matter

[0061] A printed matter on which are printed letters, figures, symbols,graphics, etc., having a thickness of 0.2 mm or more can be provided byprinting the printing ink of the present invention described above in aprescribed shape on the surface of a printed base material using adispenser, followed by curing by irradiating with light.

[0062] The present invention is particularly suitable for obtaining aBraille printed matter, and the Braille printed matter in which Braillecharacters are printed on a surface can be provided by printing theprinting ink of the present invention on the surface of a printed basematerial in the form of dots followed by curing.

[0063] In addition, a printed matter in which names, figures and soforth having a thickness of 0.2 mm or more are printed on the surface ofthe printed base material can be provided by printing the printing inkof the present invention onto the surface of the printed base materialin the form of letters, figures or symbols followed by curing.

[0064] Base materials of any materials can be used for the printed basematerial, examples of which include paper, plastic, glass, metal;ceramics, wood or composite materials thereof.

[0065] In addition, although any form of the printed base material maybe used, cards on which names, card numbers, etc., are printed, forexample, are preferable as a printed base material. In addition, thepresent invention is particularly preferable in the case of using cardsin the form of IC cards in particular, for which embossing has the riskof causing disconnection of internal IC and wiring patterns, for theprinted base material.

[0066] In addition, although the light that is emitted for curing theprinting ink specifically refers to an ultraviolet light, an electronbeam, etc., the light is not limited to these.

[0067] Printer

[0068] Next, an explanation is provided for the preferable structure ofthe printer of the present invention that is used when performing thickfilm printing using the previously described printing ink of the presentinvention.

[0069]FIG. 1 shows a schematic cross-sectional view of a printer of oneembodiment as claimed in the present invention, and explains thestructure of this printer along with the method by which printing isperformed using this printer. In the present embodiment, the explanationuses an example of a printer capable of printing Braille characters.Furthermore, the printer shown in FIG. 1 is only one example of such aprinter, and the present invention is not limited to this.

[0070] A printing section 51, which prints the photo-curable printingink onto the surface of a printed base material 20, and a curing section52, which cures the printing ink that has been printed onto the surfaceof the printed base material 20, are provided within a printer 1. Thisprinting section 51 is provided with an ink discharge unit 10, and afirst base material holding unit 31 that holds the printed base material20, while the curing section 52 is provided with a light emitting unit40 and a second base material holding unit 32 that holds the printedbase material 20.

[0071] In addition, in the printer 1 of the present embodiment, the inkdischarge unit 10, the first base material holding unit 31, a positioncontrol unit to be described later, the light emitting unit 40 and thesecond base material holding unit 32 are all contained in a single rack50.

[0072] A printed base material insertion port 61, which supplies theprinted base material 20 to the inside of the printer 1, is provided atthe left end as shown in the drawing of the rack 50, and the printedbase material 20 inserted from this printed base material insertion port61 is led to a printing section 51 by being transported in a state inwhich it is held by the first base material holding unit 31.

[0073] The ink discharge unit 10 is composed of a dispenser, and isroughly composed of an ink cylinder 11 in which the printing ink isfilled inside, and a discharge port 12 from which the printing ink isdischarged. In addition, the ink discharge unit 10 is connected to aposit-on control unit (not shown). A structure is employed that allowsthe ink discharge unit 10 to be moved three-dimensionally and arrangedat a prescribed location by the position control unit.

[0074] In the printing section 51, the position of the ink dischargeunit 10 is set by the position control unit in the state in which theprinted base material 20 is held by the first base material holding unit31. At this time, the position of the ink discharge unit 10 is set sothat a prescribed location on the surface of the printed base material20 is arranged in opposition to the discharge port 12 of the inkdischarge unit 10 while separated by a prescribed interval. Next,printing is carried out by discharging the printing ink onto theprescribed location on the surface of the printed base material 20 fromthe ink discharge unit 10.

[0075] A mechanism that causes the printing ink to be discharged byapplying pneumatic pressure to printing ink filled in the ink cylinder11 can be employed for the mechanism by which a prescribed amount of theprinting ink is discharged from the ink discharge unit 10.

[0076] After repeatedly adjusting the position of the ink discharge unit10 and printing for all locations at which printing is to be carried outon the surface of the printed base material 20, printed base material 20is transported to the curing section 52. Furthermore, in FIG. 1, theprinting ink printed onto the surface of the printed base material 20 isindicated by reference numeral 70.

[0077] The printed base material 20 that has been transported to thecuring section 52 is held by the second base material holding unit 32,and the printing ink 70 printed with the printing section 51 is cured.Curing of the printing ink 70 is carried out by emitting light onto theprinting ink 70 printed onto the surface of the printed base material 20from the light emitting unit 40 provided at a prescribed location withinthe curing section 52. Curing of the printing ink 70 may also be carriedout by transporting the printed base material 20 from left to right asshown in the drawing or by maintaining the printed base material 20 in astationary state.

[0078] In the printer 1 of the present embodiment, the light emittingunit 40 is preferably composed of an ultraviolet light source capable ofemitting ultraviolet light having an intensity of 1500 to 5000 μW/cm².By using the light source capable of emitting ultraviolet light of lowintensity as compared with a mercury, etc., in this manner, in additionto being able to reduce damages to the printed base material 20 causedby ultraviolet light and heat, the ultraviolet radiation unit can bemade to be more compact. As a result, the portable, compact printer 1can be provided in which the ink discharge unit 10, the first basematerial holding unit 31, the position control unit, the light emittingunit 40 and the second base material holding unit 32 can all becontained within the single rack 50.

[0079] Following completion of curing of the printing ink 70, theprinted base material 20 is transported by the second base materialholding unit 32 and is ejected by being discharged from a printed basematerial ejection port 62 provided in the right end as shown in thedrawing of the rack 50.

[0080] In addition, in the printer 1 of the present embodiment, lightsuch as ultraviolet light capable of curing the printing ink is blockedin the printing section 51. As a result of employing this type ofconstitution, together with being able to prevent the printing ink frombeing cured from the time the printing ink is discharged from the inkdischarge unit 10 until it reaches the printed base material 20,deterioration of the printing ink contained within the ink dischargeunit 10 can also be prevented.

[0081] Furthermore, although an explanation has only been provided forthe printer capable of printing Braille characters in the presentembodiment, the present invention is not limited to this, but rather,can also be applied to cases of printing all shapes of letters, figures,symbols, graphics, etc.

[0082] For example, in the case of printing letters, figures, symbols,etc., various shapes of thick films, such as letters, figures andsymbols, can be printed by using an ink discharge unit similar to thatof the present embodiment, and relatively moving the printed basematerial two-dimensionally while continuously discharging the ink fromthe ink discharge unit in the state in which the discharge port of theink discharge unit and the surface of the printed base material are heldseparated by a prescribed interval.

[0083] In addition, in the present embodiment, although a constitutionis employed in which a prescribed location on the surface of the printedbase material 20 and the discharge port 12 of the ink discharge unit 10are arranged in opposition separated by a prescribed interval bycontrolling the position of the ink discharge unit 10 with the positioncontrol unit, the present invention is not limited to such aconstitution. Instead, a constitution may be employed in which theposition of the ink discharge unit 10 is fixed, while the position ofthe printed base material 20 can be controlled with the position controlunit.

[0084] In addition, the present embodiment employed a constitution inwhich the printed base material 20 is transported to the curing section52 where the printing ink is cured after the printing ink was printed atall locations desired to be printed on the surface of the printed basematerial 20, the present invention is not limited to such aconstitution. Instead, printing with the printing section 51 and curingwith the curing section 52 may be repeatedly carried out alternatelywith respect to the single printed base material 20 by, for example,first printing one or a plurality of locations among the locationsdesired to be printed on the printed base material 20, transporting theprinted base material 20 to the curing section 52 for curing, and thenagain returning printed base material 20 to printing section 51 whereother locations are then printed.

[0085] In addition, in the case of desiring to print multiple types ofthe printing ink having different colors, etc., printing may be carriedout using the single ink discharge unit 10 while changing the printingink filled inside, or printing may be carried out using a plurality ofthe ink discharge units 10 and filling with each different type of theprinting ink.

[0086] In addition, although the printing section 51 and the curingsection 52 are composed separately in the present embodiment, thepresent invention is not limited to this, but rather the printingsection and the curing section may be also be composed within the samespace. For example, a constitution may be employed in which the lightemitting unit is arranged near the ink discharge unit, light is notemitted from the light emitting unit when printing with the inkdischarge unit, while the light emitting unit is turned on followingprinting with the ink discharge unit to cure the printed ink.

[0087] In addition, the printer of the present invention is preferablyused when carrying out thick film printing using the printing ink of thepresent invention. However, since the dispenser is able to dischargeinks having a broad range of the viscosities, and various units otherthan a dispenser can be used for the ink discharge unit (such as an inkjet system), the printer of the present invention can also be applied tocases of carrying out printing using various inks other than theprinting ink of the present invention.

EXAMPLES

[0088] The following provides an explanation of embodiments of thepresent invention.

[0089] (Printing Ink Composition)

[0090] In Examples 1 through 6, printing inks were prepared by usingurethane-based acrylate monomer and urethane-based acrylate prepolymerfor the photo-curable high polymer precursor,2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propane-1-one (NagaseIndustries, trade name: “Irgacure 907”) for the photopolymerizationinitiator, a benzyldimethylketal-based sensitizer for the curingaccelerator, and silicon oxide fine particles having a mean particlesize of 0.02 μm for the inorganic fine particles.

[0091] In Examples 1 through 6, printing inks were prepared by using thesame blending ratios for the urethane-based acrylate monomer,urethane-based acrylate prepolymer, photopolymerization initiator, andcuring accelerator while changing only the concentration of theinorganic fine particles.

[0092] The compositions of each printing ink prepared in Examples 1through 6 are shown in Table 1.

[0093] As shown in Table 1, in Examples 1 through 6, printing inks wereprepared by blending 55 parts by weight of urethane-based acrylatemonomer and 45 parts by weight of urethane-based acrylate prepolymer,followed by adding the inorganic fine particles while changing theamount added within the range from 3.5 to 7.0 parts by weight withrespect to 100 parts by weight of the high polymer precursor containingurethane-based acrylate monomer and urethane-based acrylate prepolymer.In addition, in Examples 1 through 6, 5 parts by weight of thebenzyldimethylketal-based sensitizer and 10 parts by weight of thephotopolymerization initiator were blended with respect to 100 parts byweight of the high polymer precursor.

[0094] (Viscoelastic Characteristics of Printing Ink)

[0095] In Examples 1 through 6, the viscoelastic characteristics of eachprinting ink obtained were measured using the Haake Model RS100rheometer. A setting of C35/1° was used for the sensor system and themeasurement temperature was 25° C.

[0096] The viscosity was measured continuously using the rheometer whilechanging shear rate. After holding for 60 seconds at a shear rate of 10(l/s), the printing ink was allowed to stand undisturbed for 120 secondswithout applying shear stress. Next, the viscosity was measured bycontinuously increasing the shear stress from 0.1 Pa to 890.5 Pa overthe course of 180 seconds, and then after allowing to stand for 30seconds at a shear rate of 890.5 Pa, the viscosity was again measured bycontinuously decreasing the shear stress from 890.5 Pa to 0.1 Pa overthe course of 120 seconds.

[0097] The relationship between the shear rate and the viscosity of theprinting ink obtained in Example 1 is shown in FIG. 2. Furthermore, inFIG. 2, the upper data in the graph indicates the data obtained when theshear rate was increased, while the lower data in the graph indicatesthe data obtained when the shear rate was decreased.

[0098] As shown in FIG. 2, the printing ink obtained in Example 1 wasdetermined to decrease in the viscosity accompanying an increase in theshear rate. Moreover, after the shear rate was increased, it wasdetermined to exhibit viscoelastic characteristics nearly identical tothose in the case of increasing the shear rate even when the shear ratewas decreased.

[0099] In addition, results similar to those of Example 1 were obtainedin Examples 2 through 6.

[0100] Therefore, in order to compare the viscoelastic characteristicsof each printing ink obtained in Examples 1 through 6, only the resultsof measuring the viscosity when the shear rate was changed from 0 (l/s)to 50 (l/s) were extracted and shown in FIG. 3. In addition, in Examples1 through 6, the viscosities of the resulting printing inks at shearrates of 5 (l/s) and 20 (l/s) are respectively shown in Table 2. Inaddition, the thixotropic index values (TI values) were calculated fromthe results obtained and also shown in Table 2. Furthermore, in Table 2,the “viscosity at a shear rate of 5 (l/s)” and “viscosity at a shearrate of 20 (l/s)” are respectively abbreviated as the “viscosity at 5(l/s)” and “viscosity at 20 (l/s)”.

[0101] As shown in FIG. 3, Table 1 and Table 2, it was determined thatas the blended amount of inorganic fine particles was increased from 3.5parts by weight to 7.0 parts by weight, in addition to the viscosityincreasing when the shear rate was small, the rate of the decrease inthe viscosity increased when the shear stress was applied, while thethixotropy became higher as the blended amount of the inorganic fineparticles was increased.

[0102] More specifically, as shown in Tables 1 and 2, as a result ofchanging the concentration of the inorganic fine particles from 3.5parts by weight to 7.0 parts by weight, it was determined that theviscosity at a shear rate of 5 (l/s) was able to be changed from 9.4(Pa·s) to 71.2 (Pa·s), while the viscosity at a shear rate of 20 (l/s)was able to be changed from 4.65 (Pa·s) to 23.6 (Pa·s). In addition, asa result of changing the concentration of inorganic fine particles from3.5 parts by weight to 7.0 parts by weight, it was determined that thethixotropic index value was able to be changed from 2.02 to 3.02.

[0103] (Printing Characteristics of Printing Ink)

[0104] Next, Braille characters were printed using the printer explainedin the previously described Example using each of the printing inksobtained in Examples 1 through 6 followed by evaluation of printingcharacteristics.

[0105] Braille characters were printed by using an air dispenser for theink discharge unit, setting the inner diameter of the discharge port to0.3 mm, the discharge air pressure to 0.3 MPa, and setting the intervalbetween the discharge port of the ink discharge unit and the surface ofthe printed base material to 0.6 mm. In addition, a fluorescent tubecapable of emitting ultraviolet light of 365 nm at an intensity of 800μm/cm² was used for the light emitting unit, while a vinyl chloride cardwas used for the printed base material.

[0106] In addition, in Examples 1 through 6, the amount of time requiredto print one Braille character (amount of time required to discharge onedrop of ink) was measured as the discharge time. In addition, the heightof the resulting Braille characters was measured after irradiating thecharacters for 3 minutes with ultraviolet light of 365 nm at anintensity of 800 μm/cm² 120 seconds after printing, and curing the inkprinted on the printed base material.

[0107] The discharge times and height of the formed characters of eachof the printing inks obtained in Examples 1 through 6 are shown in Table2.

[0108] As shown in Table 2, in Examples 1 through 6, all discharge timeswere from 0.3 to 2.0 (sec), indicating that ink droplets were able to bedischarged in a short time, and Braille characters were able to beformed having a thickness of 0.3 mm or more. In Examples 2 and 3 inparticular in which the blended amounts of the inorganic fine particleswere 4 to 4.5 parts per weight, the shape of the dots was roughlyhemispherical, and Braille characters were able to be formed that wereaesthetically superior.

[0109] Furthermore, although only the case of using vinyl chloride cardsfor the printed base material is explained in Examples 1 through 6, theinventor of the present invention has confirmed that similar results arealso obtained in the case of using cards made of PET-G or ABS(acrylonitrile-butadiene-styrene copolymer) resin, etc.

[0110] In addition, although only the case of using silicon oxide fineparticles having a mean particle size of 0.02 μm is explained inExamples 1 through 6, the inventor of the present invention hasconfirmed that similar results are also obtained in the case of usingcarbon black fine particles, aluminum oxide fine particles, iron oxidefine particles or silicon oxide fine particles having a mean particlesize of 0.1 μm or less.

[0111] In addition, the inventor of the present invention has alsoconfirmed that, in the case the concentration of inorganic fineparticles is less than 3 parts by weight, the printing ink spreadsexcessively immediately after being printed on the surface of theprinted base material, and dots having a thickness of 0.2 mm or morecannot be formed. In addition, it has also been confirmed that in thecase in which inorganic fine powder is blended in an amount greater than8 parts by weight, the discharge time required to discharge one drop ofink increases to 2.5 seconds or more, and together with lowering the inkdischarge rate to a degree that prevents it from being used practically,makes it difficult to obtain characters of a desired shape due to theformation of sharp ends as a result of the ink failing to spread afterbeing discharged onto the surface of the printed base material. TABLE 1Ink Composition Photo- Inorganic poly- fine merization MonomerPrepolymer particles initiator Sensitizer (parts by (parts by (parts by(parts by (parts by weight) weight) weight) weight) weight) Example. 5545 3.5 10 5 1 Example. 55 45 4.0 10 5 2 Example. 55 45 4.5 10 5 3Example. 55 45 5.0 10 5 4 Example. 55 45 6.0 10 5 5 Example. 55 45 7.010 5 6

[0112] TABLE 2 Viscoelastic Printing Characteristics CharacteristicsViscosity Viscosity Discharge Character at 5 (l/s) at 20 (l/s) TI valuetime height (Pa · s) (Pa · s) (−) (sec) (mm) Example. 1 9.4 4.65 2.020.3 0.38 Example. 2 12.5 5.8 2.16 0.5 0.45 Example. 3 17.8 7.4 2.4 0.60.56 Example. 4 28.2 10.7 2.64 0.9 0.67 Example. 5 44.6 15.0 2.97 1.50.82 Example. 6 71.2 23.6 3.02 2.0 0.91

INDUSTRIAL APPLICABILITY

[0113] According to the present invention, a printing ink can beprovided that allows the obtaining of a thick film of 0.2 mm or more ina single printing without causing a decrease in the discharge rate ofthe ink. According to the printing ink of the present invention, sinceprinting can be carried out without causing a decrease in the dischargerate of the ink and repeated printing is not required, a thick film canbe printed rapidly.

[0114] In addition, according to the printing ink of the presentinvention, since it is not necessary to mechanically deform the printedbase material such as by performing embossing, thick film printing canbe carried out without affecting the printed base material.

[0115] In addition, according to the present invention, the printedmatter obtained using the printing ink of the present invention, theprinting method for carrying out printing using the printing ink of thepresent invention, and the portable, compact printer suitably used whenperforming thick film printing using the printing ink of the presentinvention, can be provided.

[0116] Furthermore, the present invention can be carried out in variousother forms without deviating from its main characteristics. Thepreviously described Examples are simply examples, and should not beinterpreted as limiting the present invention. In addition, the scope ofthe present invention is indicated by the claims, and is not restrictedin any way by the description text. In addition, variations andmodifications belonging to the overall scope of claims are all includedwithin the scope of the present invention.

1. A printing ink characterized by comprising: a photo-curable highpolymer precursor and a photopolymerization initiator; wherein, at 25°C., the viscosity at a shear rate of 5 (l/s) is 8 to 75 (Pa·s), theviscosity at a shear rate of 20 (l/s) is 3 to 25 (Pa·s), and thethixotropic index value is 1.5 to 3.5.
 2. The printing ink according toclaim 1, characterized in that inorganic fine particles are additionallycontained.
 3. The printing ink according to claim 2, characterized inthat the inorganic fine particles are contained at 3 to 8 parts byweight to 100 parts by weight of the high polymer precursor.
 4. Theprinting ink according to claim 2, characterized in that the meanparticle size of the inorganic fine particles is 0.1 μm or less.
 5. Theprinting ink according to claim 2, characterized in that the inorganicfine particles are dispersed in the form of a colloid.
 6. The printingink according to claim 1, characterized by transmitting light aftercuring.
 7. A printed matter characterized in that a printing inkcomprising: a photo-curable high polymer precursor and aphotopolymerization initiator, and at 25° C., having a viscosity of 8 to75 (Pa·s) at a shear rate of 5 (l/s), a viscosity of 3 to 25 (Pa·s) at ashear rate of 20 (l/s), and a thixotropic index value of 1.5 to 3.5, isprinted on the surface of a printed base material followed by curing. 8.The printed matter according to claim 7, characterized in that theprinting ink additionally contains inorganic fine particles.
 9. Theprinted matter according to claim 8, characterized in that the printingink contains the inorganic fine particles at 3 to 8 parts by weight to100 parts by weight of the high polymer precursor.
 10. The printedmatter according to claim 8, characterized in that the mean particlesize of the inorganic fine particles is 0.1 μm or less.
 11. The printedmatter according to claim 8, characterized in that the inorganic fineparticles are dispersed in the form of a colloid.
 12. The printed matteraccording to claim 7, characterized in that the printing ink transmitslight after curing.
 13. The printed matter according to claim 7,characterized in that the printing ink is printed on the printed basematerial in a shape of a letter, a figure, or a symbol, followed bycuring.
 14. The printed matter according to claim 7, characterized inthat the printed base material is a card.
 15. The printed matteraccording to claim 14, characterized in that the printed base materialis an IC card containing an internal IC and a wiring pattern.
 16. Aprinting method characterized by comprising: a step of printing theprinting ink according to claim 1 onto a surface of a printed basematerial using a dispenser, and a step of curing the printing inkprinted onto the surface of the printed base material by exposing tolight.
 17. A printer characterized by comprising: an ink discharge unit,which has a discharge port that discharges a photo-curable printing ink,a base material holding unit, which holds a printed base material, aposition control unit, which is capable of arranging, in opposition, ata prescribed interval, the discharge port of the ink discharge unit anda prescribed position on a surface of the printed base material held bythe base material holding unit, and a light emitting unit, which curesthe printing ink by emitting a light onto the printing ink dischargedfrom the ink discharge unit onto the surface of the printed basematerial; wherein, the ink discharge unit, the base material holdingunit, the position control unit and the light emitting unit are allcontained in a single rack.
 18. The printer according to claim 17,characterized in that the ink discharge unit comprises a dispenserhaving an ink cartridge filled with the printing ink.
 19. The printeraccording to claim 17, characterized in that the light emitting unit iscapable of emitting an ultraviolet light having an intensity of 1500 to5000 μW/cm².